1. Field of the Invention
This invention relates generally to fasteners and more particularly to expanding or expandable anchor fasteners for fastening objects with respect to a wall or the like.
2. Description of the Prior Art
There are a wide variety of anchor fasteners for fastening objects with respect to a wall or the like. The most common of these anchor fasteners is known generally as a spring wing toggle bolt. This type of anchor fastener has a pair of opposed wings which are hingedly connected to each other by a hinge piece having a threaded hole therein. A bolt is positioned through the threaded hole such that the wings can be threadedly moved along the bolt. A wire spring is extended about the hinge to the move the wings to an open position. To use the spring wing toggle bolt the wings are collapsed about the bolt such that the wings and bolt can be inserted through a hole and a wall. Once through the wall the wings spring open and are drawn back against the wall. By tightening the bolt with the wings held against the wall an object connected to the bolt can be anchored to the wall.
In order to make spring wing toggle bolts sufficiently strong to withstand threaded tightening and the leverage placed upon the wings at the hinge point because the wings span the hole in the wall, the wings are generally formed of channel shaped pieces of metal. The channels extend about the bolt when the wings are collapsed to a closed position. The base portion of the wings engage each other when the wings are in an open position and prevent the wings from axially moving beyond an open position as the wings are tightened against the wall.
Spring wing toggle bolts have generally been found to be satisfactory except for a few deficiencies. One of the most important of these deficiencies is the complexity and cost. Because the spring wing toggle bolt has many pieces which must be assembled and because these pieces must be separately formed and fit together with relatively close tolerances they are relatively more expensive than other types of fasteners. Moreover, spring wing toggle bolts can be unsatisfactory for certain uses. For example, when used in connection with gypsum wallboard the channel shaped wings can cut the wallboard weakening the anchorage and can even cause complete failure of the anchorage with very little stress placed on the anchor.
In addition to spring wing toggle bolts there are a wide variety of other types of expansion anchors. Among these are the rawl drive expansion plugs and wedge driven expanding shields. There are also single wing toggle bolts which pivot about a threaded hinge. Generally, however, these devices are as complicated or more complicated than the spring wing toggle bolt and suffer from the same types of deficiencies and problems.